In recent years, miniaturization and lightening have acceleratively advanced in a notebook-size personal computer or a portable electronic device selectively having functions of a telephone, camera, GPS, radio, television and the like, and a lithium secondary battery is preferably used.
The lithium secondary battery is a secondary battery in which a lithium transition metal composite oxide is used in a (cathode) active substance of a cathode plate, a carbonaceous material is used in an (anode) active substance of an anode plate, and a nonaqueous electrolytic solution obtained by dissolving a lithium ion electrolyte in an organic solvent is used in an electrolytic solution, respectively. The battery has a characteristic that an energy density is large because an electric cell voltage is about 4 V and high. Since the battery is miniaturized and its voltage is raised owing to the characteristic as compared with a conventional secondary battery, the battery is not limited to the above-described application, the battery is also noted as a power supply for driving a motor of an electric car or a hybrid electric car that is positively and generally spreading as a low-emission car in the background of a recent environmental problem, and the application of the battery is enlarged more.
With the enlargement of the application, enhancement of safety is required for the lithium secondary battery. Since the lithium secondary battery having a high energy density and a large capacity has a large absolute value of accumulated energy, a risk in a case where the battery is improperly used is high. Therefore, it is necessary to secure sufficient safety at a handling or charging/discharging time.
According to the Battery Association of Japan, as an improper use test of a safety evaluation standard guideline of the lithium secondary battery, “nail sticking test” is specified in which a metal rod is driven into an electrode member inside the fully charged battery, and the cathode plate and the anode plate in the electrode member are internally short-circuited. It is determined that the safety should be secured without ignition, explosion or the like of the battery even in a case where an abnormal current rapidly flows. Moreover, to clear the nail sticking test, as shown in FIG. 8, assuming a case where heat is generated by the abnormal current, the electrolytic solution is evaporated, and a battery inner pressure rises, the lithium secondary battery 31 is provided with a pressure releasing mechanism 32 which allows the release of the battery inner pressure to an atmospheric air pressure (see, e.g., Patent Document 1).
Moreover, as shown in FIG. 9, a drop of battery performance is sometimes caused unless gas purging is sufficiently secured in a case where a gas is generated inside inner electrode members (electrode structures 42). To solve the problem, there is disclosed a lithium secondary battery 41 in which a plurality of collector-foil-side pores 43 are made in a cathode-side collector foil and an anode-side collector foil constituting the electrode structures 42, a plurality of core-side pores 45 are also made in a core 44 for taking up these collector foils, and the gas generated in the electrode structures 42 are released by the collector-foil-side pores 43 and the core-side pores 45 (see, e.g., Patent Document 2). It is to be noted that in FIG. 9, reference numeral 46 denotes a battery case.    [Patent Document 1] Japanese Patent Application Laid-Open No. 9-92249    [Patent Document 2] Japanese Patent Application Laid-Open No. 10-162801